(1) Field of the Invention
The present invention relates to silica gel and more particularly to a silica gel of improved hardness and abrasion resistance as well as of an increased adsorption power and other valuable properties, to a highly economic process of making such a silica gel, to an apparatus and manufacturing system for making such a silica gel, and to advantageous methods of using same.
(2) Description of the Prior Art
It is known to produce silica gel by precipitation of silicic acid containing starting materials such as waterglass and an acid, usually hydrochloric acid or sulfuric acid, whereby as an intermediate product an unstable silicic acid containing sol is obtained. Said sol is subsequently caused to gel. The salts present therein are removed from said gel by washing, and the gel is finally dried.
Heretofore, waterglass solutions of a silicon dioxide content between about 13% and about 15% were used as starting materials. Solutions of such silicon dioxide concentration yield silicic acid containing sols with about 10% of silicon dioxide. However, it was not possible to use waterglass solutions of a higher concentration in technical operation because in this case undesired precipitation of silicic acid or even premature gelling takes place at higher concentrations. As a result thereof, the manufacturing process would have to be interrupted or even discontinued and the silica gel produced would be of inferior quality due to the presence of the precipitated silicic acid flakes. The use of waterglass of a higher concentration, however, would be desirable because in this case the expenses and costs for evaporating the water as well as considerable energy expenditure would be saved and thus the manufacturing process would be more economical.
Silica gels produced according to known processes furthermore, do not have the hardness required for prolonged use in manufacturng process and the necessary abrasion resistance. They have also only a limited adsorption potential.